AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI+NS-TuA

Invited Paper MI+NS-TuA7
Magnetic Nanostructures Made by Self-assembled Block Copolymer Lithography

Tuesday, November 4, 2003, 4:00 pm, Room 316

Session: Self Assembly and Nanomagnetism
Presenter: C.A. Ross, Massachusetts Institute of Technology
Authors: C.A. Ross, Massachusetts Institute of Technology
J.Y. Cheng, Massachusetts Institute of Technology
H.I. Smith, Massachusetts Institute of Technology
E.L. Thomas, Massachusetts Institute of Technology
G. Vancso, University of Twente, The Netherlands
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The fabrication and magnetic properties of thin-film particles with diameters of 35 nm and periodicity of 50 nm made using block copolymer nanolithography will be described. Such particle arrays may be used in magnetoelectronic and magnetic storage devices, where it is important to control the magnetization state, switching field, and uniformity of the particles and to understand their size-dependent magnetic behavior. Arrays of single-layer Co and NiFe particles with thicknesses of 5, 10, 15 and 20 nm, and Co/Cu/NiFe multilayer particles have been made. The Co and NiFe particles show an increase in coercivity and a decrease in switching field distribution with thickness. The particles exhibit thermally-assisted reversal, with switching volumes larger than the physical particle volume due to strong magnetostatic coupling between the particles. The multilayer particles show hysteresis behavior consistent with interlayer magnetostatic coupling, and measurable giant magnetoresistance despite the small dimensions of the particles. These arrays have short-range close-packing, but no long-range order. To impose long-range order the substrates have been patterned with shallow grooves, which induce alignment of the rows of polymer features parallel to the steps creating an ordered array. The polymer domain spacing conforms to the dimensions of the templating features leading to a quantized number of rows of domains within each groove. It is also possible to confine the polymer to certain regions of the substrate using soft printing methods, which also leads to a limited degree of ordering. Results from these templated self-assembly processes will be discussed. This work was supported by NSF. Refs: Cheng et al, Adv. Mater. 13 1174 (2001); Appl. Phys. Letts. 81 3657 (2002); IEEE Trans. Magn. 38 2541 (2002).